The present invention relates broadly to a pressure regulating apparatus, and in particular to a coolant pressure regulating apparatus.
The state of the art of pressure regulating means is well represented and alleviated to some degree by the prior art apparatus and approaches which are contained in the following U.S. Patents:
U.S. Pat. No. 3,091,924 issued to Wilder, Jr. on June 4, 1963; PA0 U.S. Pat. No. 4,643,356 issued to Holler et al on Feb. 17, 1987; and PA0 U.S. Pat. No. 4,742,961 issued to
Starke on May 10, 1988.
The Wilder, Jr. patent is directed to a nozzle which includes a lining member that defines a throat. An array of perforations extend through the liner member both within and without a series of flaps. The flaps are arranged around the throat to be opened and closed to vary the porosity of the throat.
The Holler et al patent describes a gas turbine exhaust nozzle that includes a cooling liner for a convergent-divergent exhaust nozzle. The exhaust nozzle has a cooling liner which is strategically positioned in the nozzle to take advantage of aerodynamic conditions along the axial length of the nozzle.
The Starke patent discloses an exhaust gas nozzle which includes a cooling air diverter unit to direct cooling air to a reverser vane isolation valve during forward thrust operation, and to a conduit, which forms part of a reverser vane access passage, during reverse thrust operation. The cooling air diverter includes a pivotal arm assembly with inner and outer flaps that are independently movable about a first common hinge, and a floating flap which is pivotable about a second hinge fastened at the outward end of the inner flap.
The gas temperatures in the exhaust portion of turbojet and turbofan engines generally exceeds the limits of materials available for constructing the casings for the turbine frame, augmentor and exhaust nozzle and because of this, heat shielding liners are used inside the casings. It is necessary to cool these liners and, in turbofan engines, the coolant is core bypass or fan flow. The fan flow, after cooling the liners, passes through the exhaust nozzle along with the primary engine flow.
There are conditions under which the fan air which flows in the annulus between the liner and casing can be considerably higher in pressure than the core pressure thus resulting in inward or buckling loading. This loading can in turn, lead to the requirement for excessive structural weight and/or complexity in the design of structurally sound liners.
This excessive inward loading on exhaust liners exists on most turbofan engines. It is severe on all engines but particularly so on advanced technology engines wherein the engine depends, for its high performance, on sustained levels of fan pressure well in excess of the core engine pressure. This pressure level is often maintained by a controlled flow mixer which regulates the flow of fan air into the core stream.
On current production engines, the fan pressure normally exceeds the core engine pressure by a relatively small amount and excessive pressure loading conditions exist only transiently. The transient conditions are none the less severe however, and have resulted in buckling of liners in service. This is a current problem the solution of which threatens to add considerable weight to the liner design. These transient conditions are brought about by any condition which results in a large reduction of core pressure relative to the fan pressure. The conditions may be intentional such as the intentional opening of the exhaust nozzle on throttle chop during high speed flight as a means of maintaining engine flow or inadvertent conditions may exist such as augmentor flameout or an inadvertently opened exhaust nozzle.
On advanced high performance engines being developed for future aircraft, the excessive inward pressure imposed on the exhaust system liner from the turbine discharge all the way back to the nozzle flaps is of a much more severe nature. The transient pressure load condition, relative to current engines, is three or four fold greater but in addition high inward liner pressures exist in normal engine operation. This is brought about by two independent requirements. First, the fan flow pressure must be maintained significantly above the core pressure over much of the operating range in order to achieve maximum engine thrust, and secondly, high pressures result from necessary coolant conservation measures. Exhaust coolant flow must be strictly conserved in order to meet the performance demands of advanced engines and a key feature in the reduction of coolant flow is the replacement of the traditional perforated liner used for suppression of burner resonance with a closed cavity suppressor. Such closed cavity suppressor with greatly reduced open area conserves coolant by eliminating the coolant flow through the conventional liner perforations.
Elimination of the flow permeable perforations also, unfortunately, eliminates an effective means of venting and relieving excess liner pressure loading in event of a sudden, inadvertent drop in core pressure. This, in turn, means that in addition to the high normal operating liner pressure load, an even higher load will exist with a reduction in core pressure brought about by any of the conditions previously described.
Advanced engine exhaust liners with their coolant conserving closed cavity suppressors just do not have sufficient open area to vent fan flow into the core, limiting the pressure difference across the liner and thus the pressure load. Currently, liners are designed to tolerate both the intentionally sustained high pressure load and also the high peak pressure conditions resulting from inadvertent reduction in core pressure but this approach results in significant penalties in structural weight and/or complex, high cost, less maintainable liners contrived to tolerate extreme loading at reasonable weight.
The coolant pressure regulating apparatus has the greatest payoff on engines on which sustained fan flow pressure can far exceed core gas pressure. However, many turbofan engines have transiently exhibited excessive fan pressure and therefore could benefit from the present coolant pressure regulating apparatus. A means is needed to greatly reduce the liner pressure loading while maintaining fan pressure level as required for high performance and also conserving exhaust system coolant flow. The present invention is intended to satisfy that need.